Key changing lock for safe deposit boxes

ABSTRACT

A changeable combination key lock for safe deposit boxes and the like, wherein a guard key is insertable into a rotatable guard key plug to set guard key tumblers to permit retracting movement of a bolt, and a renter&#39;&#39;s key is insertable into a rotatable renter&#39;&#39;s key plug for engagement with normally coupled segmented tumblers to aline them to permit retraction of the bolt. A cam member is provided to be actuated by a change key which is inserted into the guard key plug when the guard key has been removed and the bolt is retracted, to disengage gating portions of the segmented tumblers from the remaining portions of such tumblers, whereupon a new renter&#39;&#39;s key may be inserted and the segmented tumblers set for the key configuration of the new renter&#39;&#39;s key.

United States Patent n91 Gartner et al.

[451 Sept. 24, 1974 KEY CHANGING LOCK FOR SAFE DEPOSIT BOXES [73] Assignee: Sargent & Greenleaf, Inc.,

Rochester, NY.

22 Filed: Apr. 9, 1973 21 Appl.No.:349,102

FOREIGN PATENTS OR APPLICATIONS 52,872

2/1942 Netherlands ..70/339 Primary Examiner--Robert L. Wolfe Attorney, Agent, or Firm-Mason, Fenwich & Lawrence [5 7] ABSTRACT A changeable combination key lock for safe deposit boxes and the like, wherein a guard key is insertable into a rotatable guard key plug to set guard key tumblers to permit retracting movement of a bolt, and a renters key is insertable into a rotatable renters key plug for engagement with normally coupled segmented tumblers to aline them to permit retraction of the bolt. A cam member is provided to be actuated by a change key which is inserted into the guard key plug when the guard key has been removed and the bolt is retracted, to disengage gating portions of the segmented tumblers from the remaining portions of such tumblers, whereupon a new renters key may be inserted and the segmented tumblers set for the key configuration of the new renters key.

11 Claims, 9 Drawing Figures BACKGROUND AND OBJECTS OF THE INVENTION The present invention relates in general to key locks, and more particularly to key locks for safe deposit boxes and the like, wherein both a guard key and a renters key having a proper configuration on the key bit must be inserted to effect retraction of the bolt.

It will be appreciated that safe deposit boxes in bank vaults and similar installations are successively leased to different parties, to whom the lessor furnishes a renter key adapted to open a given safe deposit box when the lock is partially operated or armed by a guard key in the possession ofthe lessor. Often. lessees fail to return the renters key at the expiration of their lease, or the lessee may lose the renters key, and it becomes necessary in such cases to change the tumbler lock so that it can be operated by a renters key bit having a different configuration. Also, even if the lessee returns the renters key at the expiration of his lease, it is desirable to change the key bit configuration to which the lock is responsive whenever the lessee of the box is changed, to prevent the otherwise possible use of an unauthorized duplicate of the renters key which may have been made before the renters key was returned.

For this reason, certain safe deposit box locks have been made in such a manner that the position of the gatings in the tumblers operated by the renters key is changeable, so that it may be adjustably set to be opened by different renters keys. The typical practice in this regard has been to provide a change key in the form of a non-round cross-section rod which is insertable into an opening in the safe deposit lock case or rear cover wall and through shaped openings in the renters key tumblers, when the safe deposit box has been activated by the old renters key. The combination change key interfits into shaped openings in one of two pivoted companion tumbler sectors for each of the renters key tumblers, all of which tumbler sectors are pivoted on a fixed tumbler post, to decouple the normally mated tumbler sectors of each of these tumbler and permit them to be recoupled in a position corresponding to the configuration of the bit of a new renters key.

An object of the present invention is the provision of a novel construction of a tumbler lock for safe deposit boxes and the like, having a first group of tumblers to be set by a guard key, and a second group of tumblers to be set by the renters key, and wherein a change key may be inserted in the key bushing for the guard key to decouple the gated portions of the renters key tumhlers from the remaining portions thereof for resetting the renters key tumblers to appropriate angular positions by a new renters key upon insertion of the latter and operation of the same in a selected manner.

Another object of the present invention is the provision ofa novel key lock of the tumbler type for safe deposit boxes and the like, having a plurality of renters key operated tumblers each having a gating section and a body section which may be selectively decoupled upon operation of a special cam by a combination change key inserted in the lock and operated in a special manner.

Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a front perspective view of a changeable lock for safe deposit boxes, embodying the present invention;

FIG. 2 is a horizontal longitudinal section view taken along the line 2-2 of FIG. 1;

FIG. 3 is a front elevation view of the safe deposit box lock, with the cover removed;

FIG. 4 is a vertical transverse section view taken along the line 4-4 of FIG. 3;

FIG. 5 is a fragmentary, exploded perspective view of a portion of the locking bolt and portions of two adjacent tumbler levers employed in the safe deposit box lock;

FIGS. 6 and 7 are elevation views of a typical guard key, and change key, respectively, for use in the lock of the present invention;

FIG. 8 is a perspective view of the bolt of the safe deposit box lock; and

FIG. 9 is a view similar to FIG. 3, showing the bolt in retracted position, with portions of tumblers shown in phantom lines.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, wherein like reference characters designate corresponding parts throughout the several figures, the key operated, tumbler type, changeable lock for safe deposit boxes of the present invention is indicated generally by the reference character l0 and comprises a lock case 11 and a cover plate 12 removable therefrom. In accordance with conventional practice, the lock case is a generally rectangular housing in the form of a forwardly opening box-like configuration to be forwardly closed by the cover plate 12, and comprises parallel top and bottom walls 13, 14, a rear wall 15, and end walls 16 and 17, the latter being inclined slightly relative to the plane normal to the rear wall 15 and having an opening therethrough, indicated at 18, through which the locking bolt 19 projects. The front cover plate 12 comprises a front panel or wall 20 having a plurality of openings by which the cover plate is fastened by screws or the like to the case 11 in forwardly closing relation to the case. The cover plate 12 has a pair of forwardly projecting horns or annular bosses 21, 22 one of which serves as the renter horn, or horn for the renter key, and the other of which serves as the horn for the guard or preparatory key, and for the combination change key when the latter is used. In the illustrated embodiment, the horn 21 is the renter horn and the horn 22 is the guard horn. These horns 21 and 22 serve as outwardly surrounding tubular bearings for the hubs or plugs, to be later described, for the keys, and extend through the customary circular openings provided therefor in the door of the conventional safe deposit box cubicle or chamber. The corners of the lock case 11 are provided with customary holes 23 extending therethrough for fastening bolts projecting into tapped openings in the conventional safe deposit chamber door to mount the assembled case and cover plate against the inner surface of the door.

The bolt 19 for the safe deposit box lock, illustrated best in FIG. 8, includes the usual heavy bolt portion 19a which projects from the lock case into a conventional keeper, and is guided by sliding engagement along its upper and lower edges with guide surfaces 18a bounding the opening 18, and includes a relatively thinner plate portion indicated at 19b extending from the thicker nose portion 190 rearwardly through the major portion of the mechanism chamber 24 of the lock casing and terminating in a yoke or bifurcated end portion defining vertically spaced upper and lower arms indicated at 19c and 190. Openings 19d and 192 are provided in intermediate portions of the locking bolt, and an integral fence 25 projects rearwardly from the thicker bolt nose formation 19a at substantially the vertical center or mid region of the bolt. A tumbler mounting post 26 projects integrally forwardly from the rear wall of the case 11 through a slot extension 19f of the opening 19g between the arms 19c and 19c of the bolt, permitting relative sliding movement of the bolt through its reciprocative path between projected and retracted positions. Two types of tumblers are mounted for pivotal movement on the tumbler posts 26 in interleaving or alternating relation One type of tumbler is referred to herein as guard key tumblers or pre-set tumblers 27, having apertures in their mid-regions which fit about the tumbler mounting post to pivot the tumblers 27 thereon. The tumblers 27 include a rearward tail portion 270 disposed in the zone of operation of the guard key, a front gated portion 27!) provided with a gating recess 27c opening through the front edge of the tumbler, and an arcuate recess 27d opening through the top edge of the tumbler. The gating recesses 270 of the pre-set or guard key tumblers 27 are designed to be alined in registry with the fence of the bolt 19 when the proper guard key is inserted in the guard horn 22 and is rotated, for example counterclockwise through 90 from the 3 oclock position, as viewed from the front of the lock, to the 12 oclock position to angularly position the guard key tumblers about the tumbler post 26 to aline their gates with the fence. The arcuate slots 27d in the guard key tumblers 27 are concentric with the axis of the tumbler posts 26 and slidably receive an arcuate lug 28 which projects forwardly from the 'rear wall 15 ofthe case.

The other type of tumbler is herein referred to as a renter tumbler or segmented tumbler and is indicated by the reference character 29. The segmented tumblers 29 are interposed between successive pairs of the preset or guard key tumblers 27, so that the two types of tumblers occur in alternation, as will be apparent from inspection of HO. 2, and the segmented tumblers each comprise a front gated section 30 having a gate recess 30a therein of substantially the same configuration as the gate recesses 27c in the pre-set tumblers 27, also designed to receive the fence 25 when all of the gating recesses are alined with each other and in the retraction path of the fence 25. The gated section of each segmented tumbler also includes an arcuate slot 30b similar to the slot 27d in tumbler 27, which slot 30/1 opens through the top edge of the front tumbler segment 30, and follows an arcuate path concentric with the axis of the tumbler post 26. The segmented tumbler 29 also includes a rear body section 31 which includes a medial portion 31a having a forwardly opening slot 3lb therein, and includes a rearwardly projecting, downwardly curved tail portion 310 and a forwardly extending arm 31d terminating in an arcuate set of serrations or teeth 3lt which intermesh with rearwardly projecting teeth 30! on the rear edge of the front gated section 30 of the segmented tumbler. The slot 31b in the medial portion 31a of the body portion 31 of the segmented tumblers receives the tumbler mounting post 26 which defines a pivot axis for pivotal movement of the segmented tumblers 29 while also permitting rearward translational movement of the rear body section 31 of each segmented tumbler under appropriate circumstances.

The center bores in the renter horn 21 and guard born 22, and alined circular apertures 15a and 15b in the rear wall 15 of the case 11 form the journal openings for the rotatable key plugs or hubs 33 and 34, each of the key plugs having a slot therein extending from substantially the axis of the plug radially through one side thereof to define the key way for the plug, indicated by the reference characters 33a and 34a. A conventional annular insert or bushing 35 may also be provided in the guard horn 22, as can be seen in FIG. 2.

Fixed tothe rear end portion of the key plug or cylinder 33 for the renters key, immediately inwardly of the interior surface of rear case wall 15, is an actuator or drive cam 36 in the form of a ring surrounding and fixed to the key cylinder 33, for example by being keyed in a slot thereof, and having a'radially extending projection or tang 36a which normally occupies the opening 19c, and which, after the guard key has been inserted and rotated to the 12 'oclock position in the key cylinders 34, is rotated clockwise from the 9 oclock position, as viewed from the front or in H6. 3, by the renters key to bring the projection 36a into engagement with the rear edge 19c of the opening l9e and force the bolt to the unlocking position of FIG. 9 withdrawing the bolt from locking relation with the keeper surface (not shown). However, rotation of the tang 36a beyond about a l oclock position is prevented, as the surfaces l9h of the bolt plate portion abut the change cam arcuate surface 370 in the normal position of the cam 37, as shown in FIG. 9, preventing full retraction of the bolt.

The change cam member is rotatably journaled on the rear end portion of the guard key cylinder 34 immediately adjacent the interior surface of the rear case wall 15 and has a cam body portion 37 provided with a forwardly opening eccentric slot 37b in a constricted rectangular portion 37d thereof and having a forwardly projecting arm member 37c which is diametrically opposite the slot and extends forwardly through the full thickness of the entire bankof tumblers at the arcuate portion 37a of the cam. A spring ball detent 38 is also provided in the body portion of the cam 37 from which the arm 370 extends and is resiliently biased into restraining relation in either of two recesses 39 in the rear wall 15 of the case to resiliently restrain the cam 37 in the normal, inactive position shown in H65. 2 and 3 or in a key change position displaced l therefrom.

The pro-set or guard key tumblers 27 are normally biased to a misalined, somewhat fanned position, for example as illustrated in FIG. 3, by a guard tumbler spring member 40 having a concave portion 40a which interfits onto a cylindrical mounting post of the case and has a plurality of spring fingers 40b separated from each other by narrow slots, pre-set to lie along slightly different inclined axes and bearing against the lower edges of the guard tumblers 27 to normally bias them to the position illustrated in FIG. 3 wherein their gating recesses 27c are out of alinement with each other and are spaced above the level of the fence 25. Similarly, a spring member 41 for the segmented tumblers has a concave base 41a interfitted about another cylindrical mounting post of the case 11 and having curved spring finger portions 41b separated laterally from each other by narrow slots and bearing against the upper edges of the body portions 31 to urge the segmented tumblers 29 to positions misaligning the gating recesses 30a relative to each other and spacing them out of alinement with the fence 25.

In the following description of operation of the lock, the key positions are indicated as viewed from the front of the lock or as viewed in FIG. 3. In the operation of the safe deposit box lock, the guard key, such for example as the key illustrated in FIG. 6 and indicated by the reference character 42, is inserted into the key cylinder or plug 34 in the guard horn 22 and is rotated from the 3 oclock position to the 12 oclock position disposing the bit of the key in a vertical plane with the shaped edge of the bit extending upwardly and bearing against the tail portions 27a of the guard tumblers 27. This insertion and movement of the guard key 42 rocks the guard tumblers 27 about the tumbler post 26 to a position alining each of the gating recesses 27c therein with each other and with the fence to accommodate retracting movement of the fence and bolt. The proper renters key is then inserted in the key cylinder 33 of the renters horn 21 and is rotated from a horizontal 9 o'clock position clockwise to the 12 oclock position to bring the key bit into engagement with the inclined lower edges 31f of the body portions 31 of the segmented tumblers to rock the segmented tumblers 29 about the tumbler post 26 to a position disposing their gating recesses 30a in registry with each other and in alinement with the fence 25. Additional rotation of the renters key clockwise from the upwardly extending 12 oclock position rotates the tang 36a of drive cam 16 into engagement with the vertical bounding surface l9e' in the bolt plate, forcing the bolt plate to theright, as viewed in FIG. 3, to retract the bolt to normal unlocking position, which is the point where movement is stopped by the change cam 37 by abutment of bolt surfaces 19h with cam surface 37a. The drive cam 36 is therefore stopped by the bolt at about the l oclock position, preventing the renter key from reaching the 3 oclock key exit position. The end portions 19c and 19c of the bolt have been moved out of their holding relation with the constructed rectangular portion 37d of change cam 37 at this unlocking position of the bolt. The spring ball detent 38 in the body portion of the change cam 37 in recess 29 prevents unintentional change cam movement.

.When a renter key combination change is desired, the lock will have to be brought to the normal unlocking condition shown in FIG. 9. The guard key 42 will be rotated clockwise to the 3 oclock key exit position and removed without returning the renters key to exit position, the guard tumblers 27 being held in alined, unlocking position by the fence 25 interfitting in the gates. A guard change key 43 is then inserted into horn 22, fitting key tongue 430 into slot 37b of the change cam 37; Rotation of the change key 43 counterclockwise from 3 oclock to 9 oclock position will effect rotation of the change cam 37, pushing spring ball detent 38 out of recess 39. A complete rotation of 180 will bring change cam arm 370 into contact with cam follower surface 310 separating segmented lever body 29 from segmented gated portion 30. The spring ball detent 38 will go into recess 39A. When the segmented lever portions 29 and 30 are decoupled and the change cam 37 is out of the holding relation with the bolt 19, (because the midregion of its constricted portion 3711 is radially shorter than portion 37a) the drive cam 36 can move the bolt a sufficient distance to reach the 180 key exit position in renter horn 21. The old renter key can then be removed from the lock since it can reach the 3 oclock position, letting segmented lever body portion 29 with spring pressure applied by spring 41 fall and rest on renter plug 33. The segmented lever portion 30 remains in unlocking position with its gating recess 30a receiving the fence 25.

A new renter key is inserted into the renter horn 21 at the 3 oclock position and rotated counterclockwise to the 12 oclock position bringing the curved end portions 19c and 19c of the bolt into contact with the change cam 37. The new renters key combination provides lift on segmented lever body portions 29. The guard change key 43 can now rotate change cam 37 clockwise out of the spring ball detent recess 39A, bringing change ca'marm 370 into contact with the cam follower surfaces of segmeted lever body portions 29 to the left of the guard plug 34, coupling segmented lever portion 29 with segmented lever portion 30 at the new key combination and coming to rest in the spring ball detent recess 39. The renter key combination change is thus completed.

It will also be appreciated that in accordance with standard practice, a set up key is provided by the manufacturer which'is a neutral key to which all changeable locks are set when shipped from the factory and when not in use by the customer or renter, so that the purchaser can initially set the safe deposit box locks to the proper setting for the initial renters keys. The insert 35 in the guard key horn has a relieved sector in its inwardly projecting rib to accommodate 90 rotation of the guard key. However, full rotation of the change key is permitted due to its second notch in its shank as shown in FIG. 7.

What is claimed is:

l. A changeable combination key lock for safe deposit boxes and the like, comprising a lock case, a locking bolt movable between projected and retracted bolt positions, a plurality of pivoted guard key tumblers having gating recesses for accommodating retraction of said bolt, a plurality of pivoted segmented tumblers having body segments and gated segments releasibly coupled therewith at variable positions, said tumblers normally occupying positions barring retraction of the bolt from projected position, a first rotatable key plug for insertion of a guard key therein to aline the guard key tumblers for retraction of the bolt, a second rotatable key plug for insertion of a renters key therein engaging said segmented tumblers and adjusting them to aline their gating recesses for retraction of the bolt and including means for moving the bolt between said positions upon rotation thereof, said tumbler body segments having cam follower surfaces, and a cam rotatably supported in the lock case adjacent said cam follower surfaces to be rotated between couple and release positions by a combination change key inserted in said first key plug, the cam having cam surfaces engageable with said cam follower surfaces upon rotation of the cam for decoupling the body segments from their companion gated segments to free the body segments to assume new positions corresponding to a new renters key selectively positioned in said second key plug.

2. A changeable combination key lock for safe deposit boxes and the like, comprising a lock case, a locking bolt movable between projected and retracted bolt positions, a plurality of pivoted guard key tumblers having gating recesses for accommodating retraction of said bolt, a plurality of pivoted segmented tumblers I having body segments and gated segments releasibly coupled therewith at variable positions, said tumblers normally occupying positions barring retraction of the bolt from projected position, a first rotatable key plug for insertion of a guard key therein to aline the guard key tumblers for retraction of the bolt, a second rotatable key plug for insertion of a renters kay therein engaging said segmented tumblers and adjusting; them to aline their gating recesses for retraction of the bolt and including means for moving the bolt between said positions upon rotation thereof, and a cam to be rotated between couple and release positions by a combination change key inserted in said first key plug for decoupling the body segments from their companion gated segments to free the body segments to assume new positions corresponding to a new renters key selectively positioned in said second key plug, said gated segments having copuling teeth, said tumbler body segments including teeth on a first end thereof releasibly intermeshed with the teeth of said gated segments and'including integral extensions at the opposite end thereof defining cam follower surfaces and said cam having a cam surface thereon for concurrently engaging said cam follower surfaces of said body segments upon rotation of the cam and retracting said body segments from .intermeshed relation with the gated segments by movement in a direction corresponding to bolt retracting movement.

3. A changeable combination key lock as defined in claim 1, wherein said guard key tumblers and segmented tumblers are pivotally mounted on a common tumbler post, said body segments having elongated slots receiving said post and accommodating decoupling retracting movement of the body segments codirectional to retracting movement of the bolt, the body segments having curved follower surfaces remote from the gated segments forming said cam follower surfaces partially encircling the axis of rotation of said cam at diametrically opposite zones about said axis, and said cam having a surface moveable into contact with said follower surfaces to a first position for retracting said body segments to a decoupled position relative to their companion gated segments and to a second position for returning the body segments to coupled relation with the gated segments.

4. A changeable combination key lock as defined in claim 1, wherein said segmented tumblers are arranged in side-by-side stacked relation collectively defining a tumbler stack, said cam member having an arm transversely spanning the whole stack of tumblers eccentric to the axis of rotation of the cam to concurrently engage portions of said body segments upon rotation of the cam to decoupling and recoupling positions.

5. A changeable combination key lock as defined in claim 2, wherein said segmented tumblers are arranged in side-by-side stacked relation collectively defining a tumbler stack, said cam member having an arm defining said cam surface transversely spanning the whole stack of tumblers eccentric to the axis of rotation of the cam to concurrently engage the cam follow surfaces of said body segments upon rotation of the cam to decoupling and recoupling positions.

6. A changeable combination lock key as defined in claim 1, wherein said segmented tumblers are arranged in side-by-side stacked relation with said guard key tumblers interleaved in alternation between each successive pair of segmented tumblers collectively defining a tumbler stack, said cam member having an arm transversely spanning the whole stack of tumblers eccentric to the axis of rotation of the cam to concurrently engage portions of said body segments upon rotation of the cam to decoupling and recoupling positions.

7. A changeable combination key lock as defined in claim 2, wherein said segmented tumblers are arranged in side-by-side stacked relation with said guard key tumblers interleaved in alternation between each successive'pair of segmented tumblers collectively defining a tumbler stack, said cam member having an arm defining said cam surface transversely spanning the whole stack of tumblers eccentric to the axis of rotation of the cam to concurrently engage the cam follow surfaces of said body segments upon rotation of the cam to decoupling and recoupling positions.

8. A changeable combination key lock as defined in claim 1, wherein said bolt and cam have confronting shoulder portions restraining said cam against movement from said couple position when said bolt occupies said projected position and freeing-said cam for movement to its release position only when the bolt is retracted.

9. A changeable combination key lock as defined in claim 2, wherein said bolt and cam have confronting shoulder portions restraining said cam against movement from said couple position when said bolt occupies said projected position and freeing said cam for movement to its release position only when the bolt is retracted.

10. A changeable combination key lock as defined in claim 1, wherein said boit includes an elongated bolt plate portion spanning the major portion of said lock case and having an opening therein accommodating said cam, said cam having peripheral interruptions defining oppositely facing shoulders, and said bolt plate portion having stop formations substantially abutting said shoulders when the bolt occupies said projected position to prevent rotation of the cam from said couple position, said stop formations being displaced from adjacent the cam when the bolt reaches retracted position to free the cam for rotation to release position.

11. Achangeable combination key lock as defined in claim 2, wherein said bolt includes an elongated bolt plate portion spanning the major portion of said lock case and having an opening therein accommodating said cam, said cam having peripheral interruptions defining oppositely facing shoulders, and said bolt plate portion having stop formations substantially abutting said shoulders when the bolt occupies said projected position to prevent rotation of the earn from said couple position, said stop formations being displaced from adjacent the cam when the bolt reaches retracted position to free the cam for rotation to release position.

* i i =l 

1. A changeable combination key lock for safe deposit boxes and the like, comprising a lock case, a locking bolt movable between projected and retracted bolt positions, a plurality of pivoted guard key tumblers having gating recesses for accommodating retraction of said bolt, a plurality of pivoted segmented tumblers having body segments and gated segments releasibly coupled therewith at variable positions, said tumblers normally occupying positions barring retraction of the bolt from projected position, a first rotatable key plug for insertion of a guard key therein to aline the guard key tumblers for retraction of the bolt, a second rotatable key plug for insertion of a renter''s key therein engaging said segmented tumblers and adjusting them to aline their gating recesses for retraction of the bolt and including means for moving the bolt between said positions upon rotation thereof, said tumbler body segments having cam follower surfaces, and a cam rotatably supported in the lock case adjacent said cam follower surfaces to be rotated between couple and release positions by a combination change key inserted in said first key plug, the cam having cam surfaces engageable with said cam follower surfaces upon rotation of the cam for decoupling the body segments from their companion gated segments to free the body segments to assume new positions corresponding to a new renter''s key selectively positioned in said second key plug.
 2. A changeable combination key lock for safe deposit boxes and the like, comprising a lock case, a locking bolt movable between projected and retracted bolt positions, a plurality of pivoted guard key tumblers having gating recesses for accommodating retraction of said bolt, a plurality of pivoted segmented tumblers having body segments and gated segments releasibly coupled therewith at variable positions, said tumblers normally occupying positions barring retraction of the bolt from projected position, a first rotatable key plug for insertion of a guard key therein to aline the guard key tumblers for retraction of the bolt, a second rotatable key plug for insertion of a renter''s kay therein engaging said segmented tumblers and adjusting them to aline their gating recesses for retraction of the bolt and including means for moving the bolt between said positions upon rotation thereof, and a cam to be rotated between couple and release positions by a combination change key inserted in said first key plug for decoupling the body segments from their companion gated segments to free the Body segments to assume new positions corresponding to a new renter''s key selectively positioned in said second key plug, said gated segments having copuling teeth, said tumbler body segments including teeth on a first end thereof releasibly intermeshed with the teeth of said gated segments and including integral extensions at the opposite end thereof defining cam follower surfaces and said cam having a cam surface thereon for concurrently engaging said cam follower surfaces of said body segments upon rotation of the cam and retracting said body segments from intermeshed relation with the gated segments by movement in a direction corresponding to bolt retracting movement.
 3. A changeable combination key lock as defined in claim 1, wherein said guard key tumblers and segmented tumblers are pivotally mounted on a common tumbler post, said body segments having elongated slots receiving said post and accommodating decoupling retracting movement of the body segments codirectional to retracting movement of the bolt, the body segments having curved follower surfaces remote from the gated segments forming said cam follower surfaces partially encircling the axis of rotation of said cam at diametrically opposite zones about said axis, and said cam having a surface moveable into contact with said follower surfaces to a first position for retracting said body segments to a decoupled position relative to their companion gated segments and to a second position for returning the body segments to coupled relation with the gated segments.
 4. A changeable combination key lock as defined in claim 1, wherein said segmented tumblers are arranged in side-by-side stacked relation collectively defining a tumbler stack, said cam member having an arm transversely spanning the whole stack of tumblers eccentric to the axis of rotation of the cam to concurrently engage portions of said body segments upon rotation of the cam to decoupling and recoupling positions.
 5. A changeable combination key lock as defined in claim 2, wherein said segmented tumblers are arranged in side-by-side stacked relation collectively defining a tumbler stack, said cam member having an arm defining said cam surface transversely spanning the whole stack of tumblers eccentric to the axis of rotation of the cam to concurrently engage the cam follow surfaces of said body segments upon rotation of the cam to decoupling and recoupling positions.
 6. A changeable combination lock key as defined in claim 1, wherein said segmented tumblers are arranged in side-by-side stacked relation with said guard key tumblers interleaved in alternation between each successive pair of segmented tumblers collectively defining a tumbler stack, said cam member having an arm transversely spanning the whole stack of tumblers eccentric to the axis of rotation of the cam to concurrently engage portions of said body segments upon rotation of the cam to decoupling and recoupling positions.
 7. A changeable combination key lock as defined in claim 2, wherein said segmented tumblers are arranged in side-by-side stacked relation with said guard key tumblers interleaved in alternation between each successive pair of segmented tumblers collectively defining a tumbler stack, said cam member having an arm defining said cam surface transversely spanning the whole stack of tumblers eccentric to the axis of rotation of the cam to concurrently engage the cam follow surfaces of said body segments upon rotation of the cam to decoupling and recoupling positions.
 8. A changeable combination key lock as defined in claim 1, wherein said bolt and cam have confronting shoulder portions restraining said cam against movement from said couple position when said bolt occupies said projected position and freeing said cam for movement to its release position only when the bolt is retracted.
 9. A changeable combination key lock as defined in claim 2, wherein said bolt and cam have confronting shoulder portions restraining said cam against movement from said couplE position when said bolt occupies said projected position and freeing said cam for movement to its release position only when the bolt is retracted.
 10. A changeable combination key lock as defined in claim 1, wherein said bolt includes an elongated bolt plate portion spanning the major portion of said lock case and having an opening therein accommodating said cam, said cam having peripheral interruptions defining oppositely facing shoulders, and said bolt plate portion having stop formations substantially abutting said shoulders when the bolt occupies said projected position to prevent rotation of the cam from said couple position, said stop formations being displaced from adjacent the cam when the bolt reaches retracted position to free the cam for rotation to release position.
 11. A changeable combination key lock as defined in claim 2, wherein said bolt includes an elongated bolt plate portion spanning the major portion of said lock case and having an opening therein accommodating said cam, said cam having peripheral interruptions defining oppositely facing shoulders, and said bolt plate portion having stop formations substantially abutting said shoulders when the bolt occupies said projected position to prevent rotation of the cam from said couple position, said stop formations being displaced from adjacent the cam when the bolt reaches retracted position to free the cam for rotation to release position. 